Blazer1

My Feedback: (1)

I have four planes with 4.8v@700mah receiver packs that I charge with two wall wart chargers that came with my two radios (JR 400 & JR SX600). I normally plug the receiver packs in a day or so before I am planning on flying to charge the batteries, this has worked well so far. I am finishing up on a plane that will use a 6v@1650mah receiver pack, I need to decide how I will charge this pack. It would be very convenient if I could use one of my wall wart chargers and just allow for a longer charge time. If this is not an option how would you recommend I charge the 6v pack? I do not mind even a couple of days charge time.

Rodney

That is a very doable option, I do it all the time. It will take longer to charge though. Since all chargers are slightly different (the values given on the nameplate are only approximate) you can determine the time required by putting an ammeter in series with the charger output with the battery connected for charging. Divide the current you get into the battery capacity, multiply by 1.6 and you will have the time required to fully charge a completely discharged or form a new battery. After that, usually an overnight charge (12 or so hours) will have the battery ready for flight the next day. Check out www.rcbatteryclinic.com for some other good tips on how to use wall warts for other than their intended uses including using the transmitter charge side of the charger for charging 5 cell receiver batteries at a higher rate (shorter charge times).

ChuckW

Your 4.8V charger won't make enough voltage for your 6V battery.

This Airtronics wall charger looks like it is rated for 6V: http://www3.towerhobbies.com/cgi-bin...?&I=LXLX84&P=0

You could also get something like this: http://www3.towerhobbies.com/cgi-bin...?&I=LXCTZ5&P=0

Or this: http://www3.towerhobbies.com/cgi-bin...?&I=LXTSA4&P=0

Also, is the 6V pack Nicad or NimH?

Blazer1

My Feedback: (1)

It would be nice to use the tx side of one of my wall warts to charge my 6v rx battery but I would rather not cut off the tx plug end. Does anyone sell an adapter?

It is NIMH battery.

DMcQuinn

My Feedback: (13)

I use only JR equipment, but I suspect you will find similar results with all brands of wall wart chargers. The ones rated at 50 mA will charge a 5-cell nimh pack at 40 mA. So yes you can just use the wall wart for both 4-cell and 5-cell packs. Rodney is right.
I do it routinely, as most of my receiver packs are now 5 cell nimh.

ChuckW

I've always been told it will not work and that makes sense to me so I've never bothered to attempt it. I can't see the 4.8v charger making enough voltage to charge a 6V battery but perhaps that's not the case. Now I'm going to have to do some more research on it.

Still, I get kinda nervous if I have any doubts about my receiver battery. I'd rather take the cautious route.

DMcQuinn

My Feedback: (13)

ChuckW - if you have a multi-meter (something that measures current). you can test this yourself. take an extension and cut the red wire and strip bach 1/2 inch of insulation from each end. connect your amp-meter in series with the charging circuit. Plug the wall wart into an outlet, plug the extension between the charger and the batery pack. With the ammeter hooked in series you will see that it is charging in the 40 - 50 mA range.

Or if you don't have an ammeter: Run the receiver until the servos stop (or get really slow). Take this fully discharged 5-cell receiver pack and charge it overnight with the wall-wart charger. Next day sit in front of the TV and run the receiver. You will quite likely find that the receiver pack has a full charge and it will take you a l;ong time to run it back down.

Blazer1

My Feedback: (1)

I have heard many people say you can not charge a 6v pack with a 4.8v wall wart and do not understand this logic? If the charger is outputting amperage, no matter how little, the pack is being charged. The only way that the pack would not eventually become fully charged is if the battery was self-discharging at a faster or equal rate to how fast it was being charged. If the wall wart is outputting 50mah where is it going, or are people saying the wall wart will not produce any power hooked to the wrong voltage battery? I am not trying to be argumentative here, truly curious.
You can load a dump truck with a table spoon if you have the patience.

DMcQuinn

My Feedback: (13)

Blazer1 - you are exactly right. The wall warts tend to put out about 50 mA no matter if the connected pack is 4-cell or 5-cell. My JR chargers charge at 18 mA on a 7-cell pack. An 8-cell pack barely charges at all and above 8 cells no charge. This is all measured on the "RX" cable from the charger. The "TX" charge circutry will of course charge 8 cells and more. I have never tested it beyond 8 cells, but I'm fairly sure it will charge 10 cells or so.

As a test, I once charged a very large pack (2150 mA) on a 10 mA constant current charger. Left it on for 215 hours or more, then discharged the pack using my Orbit Microlader discharger. Sure enough it was fully charged.

chashint

I charge 6v rx packs with the 4.8v wall wart and it works like a charm.

ChuckW

Well, it would have to put out enough voltage to force current into the pack. Without voltage you get no current (Amps). That's why I assumed it wouldn't work. After doing some reading and testing the voltage on an actual wall charger, I can see that it produces out more than the label says. Enough in fact to charge a 6V battery. Learn something new all the time I suppose.

I'm still not a big fan of wall chargers though and prefer to use something else but that's not relevant to the original question asked. I guess he could use the existing wall cherger if he really wanted to.

DMcQuinn

My Feedback: (13)

yes. In fact, if you try to measure the voltage coming out of the wall wart without any pack connected, you may get readings all over the place. But when you connect a pack, you get a voltage that is reasonable for that pack (within reasonable limits).

Rodney

All the wall warts I have ever tested have an open circuit voltage quite a bit higher than 7 volts. What limits the current is the internal impedance of the charger itself (the resistance in the wires in the transformer, any connections etc. The IR drop in this impedance lowers the voltage and limits the current when a battery is attached. As long as that open circuit voltage (no battery connected) is higher than the fully charged voltage of the battery, it will charge the battery.

Stick 40

We were charging the 6v packs with the wall 50 Mah charger for the last 20 years and it works.

I just tested one , I watched the voltage level while I charged my JR 2300 Mah 6v MI-MH pack and it charged up to a peek voltage of 7.25 volts using a 110 Mah wall charger and then came down to around 7 volts with a load on it for 5 min. I charged the same pack with a 6 volt field charger at 800 mah rate and it charged up to 7.55 volts peek voltage and then came down to around 7.1v with a load on it for 5 min. The only difference I can see is the time it takes to get to full charge and I think the batterys will last longer when its charged at the low rate and not over charged too long at a high rate.

Campgems

Back in 1969 I built my Royal clasic from parts. What I didn't have was a charger. After some investigation, I found that the voltage of the charger output wasn't relevant as long as you could force 1/10th the batterys MAH into the battery. SO, I bullt my charger and it was nothing more than a diode and a current limiting resistor to limit to the maximum charge rate. Really simple, untill you happened to plug the charge cord in backwards and put 110VAC on the TX case. Still charged the battery along with the pilot.

The issue with the NIMh batteries is that they don't build up the resistance at full charge like a NiCad does, so when you reach peak, it keeps trying to take a charge, over heats and then goes sour. That is why a lot of the better chargers have a temp probe. Keeps from frying the battery. My first NiMh TX battery died about three minutes into it's first flight because I left it on the wall wart for two days to make sure it was fully charged. It looked good a take off, but the alarm went off a few mintues later.

Don